If you tell them "Pursuant to consumer protection law, I hereby notify you not to call me" or something like that, They can't call you. They aren't supposed to harrass you, but thats harder to stop. I'm surprised you haven't had more like this one.
On the other hand, you should call PCC (or whoever the actual debt is) and some kind of account number or address and send them a token payment directly, and try to stay on top of it. A co-worker of mine had her paycheck garnished without warning on her rent day ... and it was an error, because she had done Americore, who was supposed to pay off the debt, but they screwed up.